The Breeding, Growth and Age Structure of a Population of the Leech Helobdella stagnalis (L.)

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Abstract
The life history of the leech Helobdella stagnalis was investigated by taking regular samples from a population on a bed of Acorus in an eutrophic lake. Leeches produced a brood in May, and then died. A proportion of their offspring were breeding in July and August, the remainder reproduced the following spring. Those leeches hatched in August also reproduced in spring. Helobdella has a marked annual rhythm of rapid growth in summer and slow growth in winter; reaches maturity at a low body weight and produces small broods. This annual rhythm corresponds with annual rhythm of growth and decay of plants on which it lives. Pattern of survival shows about 95% mortality in the 1st 3 months of life, followed by period of reduced mortality. Biotic potential of Helobdella is high which accounts for its being the most numerous spp. in eutrophic lakes.

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